Devices and Methods for Using Controlled Bubble Cloud Cavitation in Fractionating Urinary Stones

ABSTRACT

A medical imaging and therapy device is provided that may include any of a number of features. One feature of the device is that it can deliver Lithotripsy therapy to a patient, so as to fractionate urinary stones. Another feature of the device is that it can deliver Histotripsy therapy to a patient, so as to erode urinary stones. In some embodiments, the medical imaging and therapy device is configured to target and track urinary stones in the patient during therapy. Methods associated with use of the medical imaging and therapy device are also covered.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 12/868,775, filed Aug. 26, 2010, which application claims thebenefit under 35 U.S.C. 119 of U.S. Provisional Patent Application No.61/237,011, filed Aug. 26, 2009, titled “Devices and Methods for UsingControlled Bubble Cloud Cavitation in Fractionating Kidney Stones”.These applications are herein incorporated by reference in theirentirety.

INCORPORATION BY REFERENCE

All publications, including patents and patent applications, mentionedin this specification are herein incorporated by reference in theirentirety to the same extent as if each individual publication wasspecifically and individually indicated to be incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to ultrasound treatment ofurinary stones. More specifically, the present invention relates tousing a combination of Lithotripsy and Histotripsy to fractionate anderode urinary stones.

BACKGROUND OF THE INVENTION

Histotripsy and Lithotripsy are non-invasive tissue ablation modalitiesthat focus pulsed ultrasound from outside the body to a target tissueinside the body. Histotripsy mechanically damages tissue throughcavitation of microbubbles, and Lithotripsy is typically used tofragment urinary stones with acoustic shockwaves.

Histotripsy is the mechanical disruption via acoustic cavitation of atarget tissue volume or tissue embedded inclusion as part of a surgicalor other therapeutic procedure. Histotripsy works best when a whole setof acoustic and transducer scan parameters controlling the spatialextent of periodic cavitation events are within a rather narrow range.Small changes in any of the parameters can result in discontinuation ofthe ongoing process.

Histotripsy requires high peak intensity acoustic pulses which in turnrequire large surface area focused transducers. These transducers areoften very similar to the transducers used for Lithotripsy and oftenoperate in the same frequency range. The primary difference is in howthe devices are driven electrically.

As shown by FIGS. 1A-1B, Histotripsy pulses comprise (usually) smallnumber of cycles of a sinusoidal driving voltage whereas Lithotripsy is(most usually) driven by a single high voltage pulse with the transducerresponding at its natural frequencies. Even though the Lithotripsy pulseis only one cycle, its negative pressure phase length is equal to orgreater than the entire length of the Histotripsy pulse, lasting tens ofmicroseconds. This negative pressure phase allows generation andcontinual growth of the bubbles, resulting in bubbles of sizes up to 1mm. The Lithotripsy pulses use the mechanical stress produced by ashockwave and these 1 mm bubbles to fracture the stones into smallerpieces.

In comparison, each negative and positive cycle of a Histotripsy pulsegrows and collapses the bubbles, and the next cycle repeats the sameprocess. The maximal sizes of bubbles reach approximately tens tohundreds of microns. These micron size bubbles interact with a tissuesurface to mechanically damage tissue.

In addition, Histotripsy delivers hundreds to thousands of pulses persecond, i.e., 100-1 kHz pulse repetition frequency. Lithotripsy onlyworks well within a narrow range of pulse repetition frequency (usually0.5-2 Hz, which is the current limit in the United States and in Europe,however higher limits up to 4-5 Hz are contemplated). Studies show thatthe efficacy and efficiency of Lithotripsy decreases significantly whenthe pulse repetition frequency is increased to 10-100 Hz. The reducedefficiency is likely due to the increased number of mm size bubblesblocking the shock waves and other energy from reaching the stone.

Prior art treatment of nephrolithiasis (urinary stones) included earlygeneration hydroelectric spark gap Lithotripters, such as the DonierHM3, which targeted a large treatment area, covering a sizeable portionof the kidney. For this reason, treatment success rates were highwithout the need for precise image guidance, yet substantial damage tothe kidney tissue within the large focal volume also occurred.Subsequent Lithotripter development was focused on reducing renal injuryby decreasing the focal volume. Some of the current third generationLithotripters use piezoelectric (PZT) transducers, such as the RichardWolf Piezolith 3000. The PZT transducer focused ultrasound in a smalltreatment region. Fluoroscope and ultrasound imaging can be utilized totarget the urinary stones prior to and during treatment. By virtue ofthe smaller focus, the newer generation Lithotripters have reducedcollateral tissue damage, but at the expense of success rates.Inaccuracies of targeting and respiratory motion of the kidneys decreasethe fraction of pulses that directly impact the targeted stone.

Histotripsy also uses focused PZT transducers but has a differentdriving system. It uses ultrasound imaging to target the focusedultrasound to the stone and monitor the treatment in real time. Thebubble clouds generated by Histotripsy show as a temporally changinghyperechoic zone on ultrasound images. The real-time guidance makes itpossible to track the stone movement and adjust the focus position, thusfurther reducing possible collateral tissue damage. As describedearlier, stone fragments produced by lithotripter vary from smallgranules less than 1.0 mm diameter to macroscopic fragments withdiameters significantly greater than 1 mm (as shown in FIG. 2A), whileHistotripsy erodes stones into fine particles smaller than 100 μm (asshown in FIG. 2B). Table 1 lists the Histotripsy and Lithotripsyparameters for comparison.

TABLE 1 Histotripsy and Lithotripsy Parameters Parameters HistotripsyLithotripsy Energy Source Short ultrasound pulses Short ultrasoundpulses Image Guidance Ultrasound Fluoroscopy, Ultrasound Peak negative~8-40 MPa ~10-25 MPa pressure Peak positive ~30-200 MPa ~50-200 MPapressure Pulse Length 3-20 cycles 1 cycle Duty Cycle ≦5% ≦0.1% PulseRepetition ≦5 kHz ≦2 Hz Frequency

Shockwave Lithotripsy is favorable in that it is a short (˜30 minute)outpatient procedure that requires only IV sedation in the vast majorityof patients. Post-operative pain generally resolves within 1-2 days.Ureteroscopy and percutaneous nephrolithotomy generally require generalanesthesia. Although ureteroscopy is an outpatient procedure, patientsoften suffer with pain and discomfort from a ureteral stent for 4-7 daysafter treatment. Disadvantages of Lithotripsy include a stone free rateof ˜65% percent 4 weeks after treatment (compared with 90-95% stone freerate in patients having percutaneous and ureteroscopic procedures) andthe necessity and occasionally discomfort of passing stone fragmentsfollowing treatment. Furthermore, urinary stones fragmented usingshockwave Lithotripsy can remain up to several mm in size and includesharp or jagged edges that make them difficult and painful to passthrough the urinary tract.

SUMMARY OF THE INVENTION

In some embodiments, a Lithotripsy-Histotripsy system is providedcomprising a first therapy transducer configured to deliver Lithotripsytherapy to a target, a second therapy transducer configured to deliverHistotripsy therapy to the target, and a control system configured toswitch between delivering Lithotripsy therapy from the first therapytransducer to delivering Histotripsy therapy from the second therapytransducer.

In some embodiments, the first therapy transducer is configured to applyacoustic pulses that operate at a frequency between approximately 50 KHzand 5 MHz, having a pulse intensity with a peak negative pressure ofapproximately 10-25 MPa, a peak positive pressure of more than 10 MPa, apulse length of 1 cycle, a duty cycle less than 0.1%, and a pulserepetition frequency of less than 2 Hz.

In other embodiments, the second therapy transducer is configured toapply acoustic pulses that operate at a frequency between approximately50 KHz and 5 MHz, having a pulse intensity with a peak negative pressureof approximately 8-40 MPa, a peak positive pressure of more than 10 MPa,a pulse length shorter than 50 cycles, a duty cycle of less than 5%, anda pulse repetition frequency of less than 5 KHz.

In some embodiments, the Lithotripsy-Histotripsy system furthercomprises an imaging system. In some embodiments, the imaging systemcomprises a fluoroscopic imaging system. In other embodiments, theimaging system comprises an ultrasound imaging system. In additionalembodiments, the imaging system comprises a combination fluoroscopic andultrasound imaging system. The imaging system can be configured totarget and track a urinary stone in a patient.

In another embodiment of a Lithotripsy-Histotripsy system, the systemcomprises a multi-mode therapy transducer configured to deliverLithotripsy therapy and Histotripsy therapy to a target, and a controlsystem configured to switch between delivering Lithotripsy therapy fromthe multi-mode therapy transducer to delivering Histotripsy therapy fromthe multi-mode therapy transducer.

In some embodiments, the multi-mode therapy transducer is configured toapply acoustic pulses that operate at a frequency between approximately50 KHz and 5 MHz, having a pulse intensity with a peak negative pressureof approximately 10-25 MPa, a peak positive pressure of more than 10MPa, a pulse length of 1 cycle, a duty cycle less than 0.1%, and a pulserepetition frequency of less than 2 Hz, so as to deliver Lithotripsytherapy to the target.

In other embodiments, the multi-mode therapy transducer is configured toapply acoustic pulses that operate at a frequency between approximately50 KHz and 5 MHz, having a pulse intensity with a peak negative pressureof approximately 8-40 MPa, a peak positive pressure of more than 10 MPa,a pulse length shorter than 50 cycles, a duty cycle of less than 5%, anda pulse repetition frequency of less than 5 KHz, so as to deliverHistotripsy therapy to the target.

In some embodiments, the Lithotripsy-Histotripsy system furthercomprises an imaging system. In some embodiments, the imaging systemcomprises a fluoroscopic imaging system. In other embodiments, theimaging system comprises an ultrasound imaging system. In additionalembodiments, the imaging system comprises a combination fluoroscopic andultrasound imaging system. The imaging system can be configured totarget and track a urinary stone in a patient.

A method of treating urinary stones is also provided, comprisingapplying Histotripsy therapy to generate a bubble cloud, positioning thebubble cloud on a urinary stone, applying Lithotripsy therapy togenerate a shock wave to fractionate the urinary stone into macroscopicurinary stone particles, and applying Histotripsy therapy to themacroscopic urinary stone particles to erode the macroscopic urinarystone particles.

In some embodiments, the positioning step further comprises positioningthe bubble cloud on a urinary stone under imaging guidance. In otherembodiments, the positioning step further comprises positioning thebubble cloud on a urinary stone under ultrasound imaging guidance. Inadditional steps, the positioning step further comprises positioning thebubble cloud on a urinary stone under fluoroscopic and ultrasoundimaging guidance.

In some embodiments, the applying Histotripsy therapy steps compriseapplying Histotripsy therapy with a multi-mode transducer. In otherembodiments, the applying Lithotripsy therapy step comprises applyingLithotripsy therapy with the multi-mode transducer.

In one embodiment, the applying Histotripsy therapy steps compriseapplying Histotripsy therapy at a first pulse repetition frequency,wherein the applying Lithotripsy therapy step comprises applyingLithotripsy therapy at a second pulse repetition frequency, the methodfurther comprising interleaving Histotripsy therapy and Lithotripsytherapy with virtually no change in the first and second pulserepetition rates.

Another method of treating a target tissue is provided, comprisingdelivering a first Lithotripsy pulse to the target tissue, delivering asequence of Histotripsy pulses to the target tissue after the firstLithotripsy pulse, and delivering a second Lithotripsy pulse to thetarget tissue after the sequence of Histotripsy pulses, wherein thefirst and second Lithotripsy pulses are separated in time by a pulserepetition frequency. In some embodiments, the target tissue is aurinary stone.

In some embodiments, the method further comprises delivering a sequenceof Histotripsy pulses immediately prior to delivering the firstLithotripsy pulse to the target tissue to suppress cavitation. Inadditional embodiments, the method further comprises delivering asequence of Histotripsy pulses immediately prior to delivering thesecond Lithotripsy pulse to the target tissue to suppress cavitation.

In some embodiments, the method further comprises delivering aspatially-varying cavitation suppressing Histotripsy field to allowcavitation to occur within the target tissue while suppressingcavitation outside the target tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a typical Histotripsy pulse and Lithotripsypulse, respectively.

FIG. 2A illustrates a urinary stone eroded by Histotripsy therapy.

FIG. 2B illustrates a urinary stone fractionated by Lithotripsy therapy.

FIG. 3 illustrates one embodiment of a Lithotripsy-Histotripsy system.

FIG. 4 illustrates a schematic view of a Lithotripsy-Histotripsy system.

FIG. 5 illustrates a pulse sequence of Lithotripsy therapy interleavedwith Histotripsy therapy.

DETAILED DESCRIPTION OF THE INVENTION

In addition to imaging tissue, ultrasound technology is increasinglybeing used to treat and destroy tissue. In medical applications such asHistotripsy, ultrasound pulses are used to form cavitationalmicrobubbles in tissue to mechanically break down and destroy tissue. InLithotripsy procedures, ultrasound pulses are used to form acousticshockwaves that break up urinary stones into smaller fragments.Particular challenges arise in using Lithotripsy to break up urinarystones, including failing to break stones down into sizes small andsmooth enough to pass comfortably, as well as visualizing and trackingthe stones within the patient. The present invention describes severalembodiments of devices and methods for treating urinary stones or othercalculi including, but not limited to biliary calculi such as gallstones, particularly through the combination of Histotripsy andLithotripsy therapy in a single procedure.

Despite the difference between Lithotripsy and Histotripsy, the aperturesize, focal characteristics, and piezoelectric materials of the relativetransducers are similar in both types of therapy. Thus, a singletransducer can be driven in both Histotripsy and Lithotripsy modes. Thisdual-mode Histotripsy and Lithotripsy system can be configured to treat,fractionate, and dissolve urinary stones in patients suffering fromurinary stones.

In some embodiments, a multi-mode Lithotripsy-Histotripsy device isconfigured to shift virtually instantaneously (electronic speeds) from aLithotripsy shock wave mode (L-mode) to the Histotripsy “soft” erosionmode (H-mode). The primary advantages of a dual modeLithotripsy-Histotripsy system are: (1) ability to rapidly fractionateurinary stones into smaller gravel like fragments in L-mode, which canbe reduced in size more quickly by H-mode erosion (erosion iseffectively a surface phenomena) because of the greatly increasedsurface area of the Lithotripsy fragments; (2) easy image guidance andinitial focal targeting by utilizing the Histotripsy bubble cloud.

Despite the differences between Lithotripsy and Histotripsy, theaperture size, focal characteristics, and piezoelectric materials of thetransducers needed for each system are similar. The circuitry andgenerators required to drive these transducers can be configured todrive a single transducer in both H and L-modes, or alternatively, canbe configured to drive separate H-mode and L-mode transducers.

FIG. 3 illustrates a combination Lithotripsy-Histotripsy system 300,comprising therapy transducer 302, therapy transducer 304, imagingsystem 306, control system 308, display 310, and patient support 312. Inone embodiment, therapy transducer 302 can be a Lithotripsy transducerconfigured to operate in an L-mode to deliver Lithotripsy therapy to atarget, and therapy transducer 304 can be a Histotripsy transducerconfigured to operate in an H-mode to deliver Histotripsy therapy to atarget. In another embodiment, a combination Lithotripsy-Histotripsysystem may include only a single transducer, such as therapy transducer302, the transducer being configured to deliver both Lithotripsy therapyand Histotripsy therapy, without requiring a second therapy transducer304. Therapy transducers 302 and 304 may have a single focus withmechanical or electromechanical steering of the respectiveLithotripsy-Histotripsy focus. Alternatively, the therapy transducersmay comprise a phased array to provide electrical steering of the focalpoint. Histotripsy transducers can be fabricated from piezo-electricceramic materials that are pulsed with high voltage electric signals atultrasonic frequencies. Lithotripsy transducers can be fabricated frompiezo-electric ceramic materials or they may be magneto-resistivemagnetic transducers or spark gap transducers, for example.

In some embodiments, Histotripsy transducers can apply acoustic pulsesthat operate at a frequency between approximately 50 KHz and 5 MHz,having a pulse intensity with a peak negative pressure of approximately8-40 MPa, a peak positive pressure of more than 10 MPa, a pulse lengthshorter than 50 cycles, a duty cycle between approximately 0.1% and 5%and in some embodiments less than 5%, and a pulse repetition frequencyof less than 5 KHz. In other embodiments, Lithotripsy transducers canapply acoustic pulses that operate at a frequency between approximately50 KHz and 5 MHz, having a pulse intensity with a peak negative pressureof approximately 10-25 MPa, a peak positive pressure of more than 10MPa, a pulse length of 1 cycle, a duty cycle less than 0.1%, and a pulserepetition frequency of less than 2 Hz.

Imaging system 306 can provide real-time imaging guidance of the patientwhile during L-mode and H-mode therapy. In the embodiment of FIG. 3,imaging system 306 comprises an ultrasound and fluoroscopic C-Armimaging system. However, due to the size and cost of C-arm imagingsolutions, in other embodiments the imaging system can comprise ahigh-resolution ultrasound imaging system. If an ultrasound imagingsystem is used, it can be separate from therapy transducers 302 and 304.Alternatively in some embodiments, the ultrasound imaging system can bedisposed on or within the therapy transducers 302 and 304. Real-timeimaging from imaging system 306 can be displayed on display 310, whichcan comprise and electronic display or a graphical user interface (GUI).In some embodiments, the display can visualize treatment from both thetherapy transducers 302 and 304 at the same time, thus having thecapability to overlap or fuse the fluoroscopic and ultrasonic images tooptimize image planning and therapy tracking. Therapy transducers 302and 304 and imaging system 306 can be packaged together as a singleunit, as shown in FIG. 3, to facilitate imaging and treatment of apatient lying on patient support 312.

Control system 308 can include all the necessary drive electronics andsignal generators necessary to drive therapy transducers 302 and 304 inboth L-mode and H-mode. For example, the drive electronics and signalgenerators of control system 308 should be configured to drive therapytransducers 302 and/or 304 according to the parameters set forth inTable 1 above for both H-mode and L-mode transducers. The control system308 can including a switching mechanism configured to instantaneouslyswitch operation of the system between an L-mode and an H-mode, or toallow for simultaneous operation in H and L-modes. Control system 308can further include a CPU or computer configured to set treatmentparameters, receive and process imaging information, and direct L-modeand H-mode therapy according to a surgical plan. The therapy transducerdrive electronics may be configured to generate both types of pulses asa pulse sequence in addition to Histotripsy pulses that optimizeLithotripsy pulses by suppressing and enhancing cavitation. One therapytransducer may have the capability of focusing outside of the target areto suppress cavitation and thereby provide active protection of tissuesoutside of the target area. This technique is more fully described inU.S. patent application Ser. No. 12/121,001, filed May 15, 2008, nowU.S. Pat. No. 8,057,408, titled “Pulsed Cavitational UltrasoundTherapy.”

FIG. 4 is a schematic drawing showing additional details of the systemof FIG. 3. Lithotripsy-Histotripsy system 400 of FIG. 4 can includetherapy transducer 402, imaging system 406, optional ultrasound imagingprobe 407, H-mode driving system 414, L-mode driving system 416, andswitching mechanism 418, which can be a physical or electronic controlswitch. In FIG. 4, therapy transducer 402 can represent either therapytransducers 302 and 304 of FIG. 3, or alternatively, can represent asingle therapy transducer capable of both H and L-mode pulses. TheLithotripsy-Histotripsy system 400 of FIG. 4 allows virtuallyinstantaneous switching between H-mode driving system 414 and the L-modedriving system 416 with electronic control switch 418 to allow aninfinite range of possibilities for time division multiplexing of theH-mode and L-mode pulses.

Methods of using a Lithotripsy-Histotripsy system, such as the systemdescribed herein, will now be discussed. The choice of modality fortreating patients with nephrolithiasis depends upon stone size, stonelocation, anatomic factors, patient factors, and patient preference. Ingeneral, for stones in the ureter or kidney having a size less than 2 cmin greatest dimension, shockwave Lithotripsy and ureteroscopy arefirst-line treatment options. For stones in the kidney (particularlythose that reside in the lower pole of the kidney), percutaneousnephrolithotomy, albeit much more invasive of a procedure, can also bean appropriate option. Shockwave lithotripsy was the primary modalityfor managing these stones; however, advances in ureteroscopicinstrumentation and technology have placed ureteroscopy on equal footingwith shockwave lithotripsy, such that this has become the preferredfirst-line therapy at many academic medical centers.

The primary advantage of Histotripsy therapy over Lithotripsy therapy isthe uniformly microscopic size of the reduced stone particles comparedto Lithotripsy. For some stones which do not break down via L-modetherapy into sufficiently small fragments to be passed through theurinary tract, this may be critical. Some situations might be bestapproached primarily in the L-mode (harder stones in places wherefragments are easily passed) and some situations might be bestapproached primarily in the H-mode (softer more easily eroded stones).Some may require a combination of each system with optimal applicationto be determined by clinical and laboratory experience with such asystem. Additionally, visualization of Lithotripsy procedures istypically challenging and requires large and expensive imagingequipment, such as a fluoroscopic C-Arm. However, cavitational bubbleclouds formed with a Histotripsy H-mode pulse can be easily viewed inreal time under ultrasound imaging. Thus, it can be possible tovisualize and target a urinary stone or by placing an H-mode bubblecloud on the stone, then focusing an L-mode shockwave towards theposition of the bubble cloud to fragment the stone.

Thus, referring back to FIGS. 3-4, one method of treating urinary stoneswith a Lithotripsy-Histotripsy system (e.g., Lithotripsy-Histotripsysystem 300/400 of FIG. 3/4) may include positioning a patient on apatient support (e.g., patient support 312 of FIG. 3) and imaging thepatient with an imaging system (e.g., imaging system 306 of FIG. 3). Theimaging system can be, for example, an ultrasound imaging system or afluoroscopic imaging system. The method can include targeting a urinarystone or urinary stones within the patient with the imaging system.Next, the method can include focusing an H-mode therapy transducer(e.g., therapy transducer 304 of FIG. 3) on the urinary stone andgenerating a bubble cloud onto the stone under the ultrasound imageguidance. The Histotripsy bubble cloud can be visualized as a greatlyenhanced backscatter region on a visual display (e.g., display 310 ofFIG. 3).

Next, the Lithotripsy-Histotripsy system can be switched to an L-modewith a switching mechanism (e.g., switching mechanism 418 of FIG. 4) todeliver a shock wave or shock waves to the urinary stone tomacroscopically fractionate the stone. Verification of the focalposition and its relationship to the urinary stone can be achieved byswitching back to H-mode and visualizing the H-mode bubble cloud underimaging guidance. Furthermore, the H-mode bubble cloud can continue toerode the macroscopic urinary stone particles due to the increasedsurface area of multiple fractionated stone particles compared to theoriginal urinary stone. The Histotripsy therapy can function to smooth(by erosion) the Lithotripsy fragments so as to facilitate passage ofthese fragments by removing sharp corners, edges, or elongateddimensions which can hinder passage of fragments through the ureter.

Thus, L-mode and H-modes of operation can be alternated so as to breakdown urinary stones into macroscopic particles (with L-mode pulses) andsubsequently erode the macroscopic particles into a fine powder (withH-mode pulses). Histotripsy and Lithotripsy are naturally complementaryas Lithotripsy shockwaves are efficient at causing initial coarsesubdivision of targeted stones which greatly increases surface area andrate for subsequent Histotripsy erosion. Since the actual position ofthe original urinary stone can be tracked by image analysis (e.g.,visual tracking of the stone itself or speckle tracking), theLithotripsy-Histotripsy system can allow for movement of the kidney andcan continually reposition the focus onto the tracked target volume.Visualization of the Histotripsy bubble cloud at the target position canconfirm proper targeting.

In some method embodiments, urinary stones can be treated solely withHistotripsy H-mode pulses. Thus, Histotripsy acoustic sequences can beapplied directly to the stones to cause erosion of the stones, producingextremely fine debris particles less than 100 μm in diameter which canbe passed painlessly by the patient and eliminate the risk ofsteinstrasse (multiple obstructing fragments within the ureter). Stillreferring to FIGS. 3-4, another method of treating urinary stones with aLithotripsy-Histotripsy system (e.g., Lithotripsy-Histotripsy system300/400 of FIG. 3/4) may include positioning a patient on a patientsupport (e.g., patient support 312 of FIG. 3) and imaging the patientwith an imaging system (e.g., imaging system 306 of FIG. 3). The methodcan further comprise targeting a urinary stone or urinary stones withinthe patient with the imaging system. Next, the method can includefocusing an H-mode therapy transducer (e.g., therapy transducer 304 ofFIG. 3) on the urinary stone and generating a bubble cloud onto thestone under the ultrasound image guidance. The Histotripsy bubble cloudcan be visualized as a greatly enhanced backscatter region on a visualdisplay (e.g., display 310 of FIG. 3). The method can further compriseapplying Histotripsy therapy to the urinary stone to erode the stoneinto fine particles having a size less than 100 μm in diameter.

Alternative embodiments of methods of treating urinary stones caninclude multi-frequency systems for additional optimization, e.g.,L-mode at higher frequencies (probably about 1 MHz) to fragment thestone and H-mode at lower frequencies (about 500 Khz) to cover the wholestone area and to make sure the increased stone surface area is usablefor enhanced surface-based erosion. Referring now to FIG. 5, sinceL-mode pulses 520 typically have a maximum pulse repetition frequency(PRF) about 2 Hz (2 pulses per second), and L-mode pulses are generallyless than 100 micro-seconds long, most of the time during L-mode therapyis available for H-mode pulses 522. In some embodiments, L-mode pulsescan have a maximum PRF of about 5 Hz. Since the H-mode PRF can be 1 kHzor larger, the H-mode pulses 522 and L-mode pulses 520 can progresstogether appropriately interleaved in time with little decrease in PRFfor either, as shown in FIG. 5. Thus during urinary stone treatment,L-mode pulses can fracture a large urinary stone into fragments toincrease the stone surface area for the H-mode, which can then progressvirtually undiminished in PRF by temporal sharing with the L-mode. Itshould be noted that the H-mode can trap fragments within its focalfield. This may allow trapping of L-mode fragments until the H-modepulses erode all fragments to very small particles that then escape thetrapping field.

This L-mode and H-mode interleaving technique can be used to treaturinary stones. Thus, referring back to FIGS. 3-5, one method oftreating urinary stones with a Lithotripsy-Histotripsy system (e.g.,Lithotripsy-Histotripsy system 300/400 of FIG. 3/4) may includepositioning a patient on a patient support (e.g., patient support 312 ofFIG. 3) and imaging the patient with an imaging system (e.g., imagingsystem 306 of FIG. 3). The imaging system can be, for example, anultrasound imaging system or a fluoroscopic imaging system. The methodcan include targeting a urinary stone or urinary stones within thepatient with the imaging system. Next, the method can include focusingan H-mode therapy transducer (e.g., therapy transducer 304 of FIG. 3) onthe urinary stone and generating a bubble cloud onto the stone under theultrasound image guidance. The Histotripsy bubble cloud can bevisualized under ultrasound image guidance as a greatly enhancedbackscatter region on a visual display (e.g., display 310 of FIG. 3).Since the bubble cloud cannot be imaged under solely fluoroscopicimaging, if no ultrasound imaging is used then the stones can betargeted by positioning the geometric focus of the therapy transducer(e.g., the expected location of the bubble cloud) on the targetedurinary stone.

Next, the Lithotripsy-Histotripsy system can generate an L-mode pulse todeliver a shock wave to the urinary stone to macroscopically fractionatethe stone. Since L-mode pulses typically have a PRF≦2 Hz (but possibly≦5 Hz), the time between subsequent L-mode pulses can be used to applyH-mode pulses, which typically have a PRF≦5 kHz. Thus, the method oftreatment can comprise delivering an L-mode pulse to a urinary stone tofractionate the stone, instantaneously switching to an H-mode ofoperation to deliver a series of H-mode pulses to the urinary stone, andinstantaneously switching back to an L-mode to deliver anotherLithotripsy shockwave to the stone(s). As described above, verificationof the stone position can be achieved by switching to H-mode andvisualizing the H-mode bubble cloud under imaging guidance.

Histotripsy can be used to enhance shockwave (Lithotripsy) fragmentationof stones through control of the cavitation environment. Histotripsy canbe used to control the cavitation environment to enhance and suppresscavitation at appropriate times. For example, Histotripsy can be used tosuppress cavitation to improve efficacy at higher Lithotripsy shockwaverates. Additionally, Histotripsy can be used to suppress cavitation inhealthy tissue to facilitate a higher Lithotripsy shockwave rate. Highrepetition rate Lithotripsy (>2 Hz) is currently limited by thepersistence of microbubbles created during the process (cavitation)which interfere with subsequent shockwaves. Simple suppression ofcavitation does not improve overall comminution because some cavitationis necessary for complete fragmentation. Time-varying Histotripsysequences applied immediately before the arrival of a Lithotripsyshockwave to suppress cavitation, followed by enhancement sequencesduring the tensile portion of the Lithotripter wave (acting as a pump)can maximize both methods of comminution. This technique can greatlyincrease the efficiency of shockwaves as well as the rate which can beused allowing more complete comminution of even difficult urinarystones.

Cavitation suppressing Histotripsy acoustic sequences can be used toreduce collateral tissue injury during high dose and high rate shockwaveapplication. Studies have shown increased risk of injury when highshockwave rates or high shockwave doses are attempted limiting thethoroughness and effectiveness of a treatment. A spatially-varyingcavitation suppressing Histotripsy field can allow cavitation to occurwithin a target zone while suppressing cavitation outside the targetzone. This technique can be used to eliminate collateral injury fromshockwaves while permitting necessary cavitation on the stone surfacewhen large shockwave doses and higher rates are used for more completecomminution. Thus, a method of treating tissue can comprise deliveringLithotripsy therapy to a target tissue to treat the target tissue, anddelivering spatially-varying Histotripsy therapy to allow cavitation tooccur within the target tissue while suppressing cavitation outside thetarget tissue.

As for additional details pertinent to the present invention, materialsand manufacturing techniques may be employed as within the level ofthose with skill in the relevant art. The same may hold true withrespect to method-based aspects of the invention in terms of additionalacts commonly or logically employed. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein. Likewise, reference to a singular item,includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe subject specification, but rather only by the plain meaning of theclaim terms employed.

What is claimed is:
 1. An ultrasound therapy system, comprising: a firstultrasound therapy transducer configured to deliver to a targetultrasound pulses having a pulse length of 1 cycle and a pulserepetition frequency less than or equal to 2 Hz; a second ultrasoundtherapy transducer configured to deliver to the target ultrasound pulseshaving a pulse length of 3-20 cycles and a pulse repetition frequencyless than or equal to 5 kHz; and a control system configured to switchbetween delivering therapy from the first therapy transducer todelivering therapy from the second therapy transducer.
 2. The system ofclaim 1 wherein the first ultrasound therapy transducer is configured toapply acoustic pulses that operate at a frequency between approximately50 KHz and 5 MHz, having a pulse intensity with a peak negative pressureof approximately 10-25 MPa, a peak positive pressure of more than 10MPa, and a duty cycle less than 0.1%.
 3. The system of claim 1 whereinthe second therapy transducer is configured to apply acoustic pulsesthat operate at a frequency between approximately 50 KHz and 5 MHz,having a pulse intensity with a peak negative pressure of approximately8-40 MPa, a peak positive pressure of more than 10 MPa, and a duty cycleof less than 5%.
 4. The system of claim 1 further comprising an imagingsystem.
 5. The system of claim 4 wherein the imaging system comprises afluoroscopic imaging system.
 6. The system of claim 4 wherein theimaging system comprises an ultrasound imaging system.
 7. The system ofclaim 4 wherein the imaging system comprises a combination fluoroscopicand ultrasound imaging system.
 8. The system of claim 4 wherein theimaging system is configured to target and track a urinary stone in apatient.
 9. An ultrasound therapy system, comprising: a multi-modetherapy transducer configured to deliver acoustic pulses to a target ina first mode in which the pulses have a pulse length of 1 cycle and apulse repetition frequency less than or equal to 2 Hz and in a secondmode in which the pulses have a pulse length of 3-20 cycles and a pulserepetition frequency less than or equal to 5 kHz; and a control systemconfigured to switch between delivering therapy from the multi-modetherapy transducer in the first mode to delivering therapy from themulti-mode therapy transducer in the second mode.
 10. The system ofclaim 9 wherein in the first mode the multi-mode therapy transducer isconfigured to apply to the target acoustic pulses that operate at afrequency between approximately 50 KHz and 5 MHz, having a pulseintensity with a peak negative pressure of approximately 10-25 MPa, apeak positive pressure of more than 10 MPa, and a duty cycle less than0.1%.
 11. The system of claim 9 wherein the multi-mode therapytransducer is configured to apply acoustic pulses that operate at afrequency between approximately 50 KHz and 5 MHz, having a pulseintensity with a peak negative pressure of approximately 8-40 MPa, apeak positive pressure of more than 10 MPa, and a duty cycle of lessthan 5%.
 12. The system of claim 9 further comprising an imaging system.13. The system of claim 12 wherein the imaging system comprises afluoroscopic imaging system.
 14. The system of claim 12 wherein theimaging system comprises an ultrasound imaging system.
 15. The system ofclaim 12 wherein the imaging system comprises a combination fluoroscopicand ultrasound imaging system.
 16. The system of claim 12 wherein theimaging system is configured to target and track a urinary stone in apatient.